This invention relates generally to the field of disc filters and in particular relates to a true running, one piece vacuum disc filter having independent controls and utilizes a caulking medium for holding the filtering media on the face of each segment of the filtering disc.
Disc filters are well known in the art and have been commonly used for filtering or separating solids from a liquid. For example, disc filters have been used for separating wood pulp from water, separating fine coal from a sludge or concentrates, separating concentrates from copper, lead, zinc, iron and uranium sludge. It is also used in the aluminum industry for separating out aluminum hydrate and in the starch industry for separating and semi-drying starch cakes prior to heat drying.
Disc filters have also been used to separate very fine particulates and immiscible liquids from aqueous solutions by use of precoating techniques.
Essentially all of the disc filters now in operation are constructed from fan shaped segments adjacently secured to produce a disc filter. The resulting disc filter is normally a non-true disc which will wobble or stray from its true zone of rotation during operation. Wobbling is especially prevalent when the segments are removed for the purpose of replacing the filter media. Most all existing disc filtering systems have from one to fourteen discs utilizing a common feed, drain, vacuum and blow discharge.
In some filtering systems, two valves are used. One located at each end of the center shaft. With this type of system at least one half of all the discs in the system must be in use during operation. However such systems are not that common.
This means that all or at least half of the discs are tied into a common system and thus all or at least one-half of the discs must be in use at one time. This also means that the filtering parameters of each of the discs cannot be individually altered. In other words, most of the discs must be started together, operated under identical conditions and that dissimilar materials cannot be filtered at the same time on the same system.
Because there is a tendency for the disc filter to wobble and stray, sophisticated and costly adjustable scraper blades must be employed to insure that most of the filter cake is evenly removed and to prevent inadvertent damage by the blade tearing into the filter media. True running discs are especially essential when an expensive precoating material is used in the filtering process. This insures that only a uniform thin layer of the precoat material is removed during the cake removal process. This insures for a more uniform filter cake and extends the time between precoatings.
One important advantage that can be realized by utilizing independent controls on a disc filtering system is that each of the discs can be started up individually and thereby permit the application of maximum vacuum to each disc during start up. During operation, the filtration rates can be altered by increasing or decreasing the vacuum. This is accomplished by increasing or decreasing the number of discs on stream and thereby compensate for dissimilar feeds or for different feed slurry concentrations. It also prevents backside blinding which is inherent in single valve filters because each disc section reports directly and individually to the vacuum source.
Another important feature of this invention is that the filter media fixed to both sides of the disc filter can be easily and readily replaced. Normally the disc filters are constructed from fan shaped segments held adjacently together by radial rods, arcuate retainer members, clamps and nuts. These rods and retainer members sometimes secure the filter media to the face of the filter segments. In other disc filters, specially fabricated filter bags are utilized to fit over the segmented sections. In either case, the filter segments must first be removed before the filter media can be installed. This limits the diameter size of the filter that can be practically used without the aid of specialized lifting equipment. In the instant invention, this is overcome by providing a continuous fan shaped groove, formed by the grooves on the radial support bars and the peripheral rim. This permits the filter media to be positioned and fixed to each of the segmented faces by means of a caulking media such as rope or polymeric tape. This facilitates replacement of the filter media as removal of the segments is not a condition precedent to replacement of the filter media.